The subject invention generally concerns test and measurement instruments, and in particular concerns those test and measurement instruments employing telecom mask features.
In the telecommunications industry, it is commonplace to perform a test to determine if a particular signal is in compliance with parameters established by national and international communications standards bodies such as ITU-T and ANSI. A primary way to perform such a compliance test is to compare the pulse shape of a waveform acquired by an oscilloscope to a waveform xe2x80x9cmaskxe2x80x9d. The mask defines a pathway having minimum and maximum amplitude values, predetermined bit rate, and defined minimum slope on signal edges (i.e., minimum bandwidth). If the signal under test stays within the pathway boundaries, then the signal passes the test. This kind of test is known as Telecom Mask Testing.
A recent innovation in oscilloscope features has been a xe2x80x9cAUTOSET TO MASKxe2x80x9d function. The AUTOSET TO MASK function automatically sets up the horizontal, vertical, and triggering settings on the oscilloscope to accommodate the expected signal, and overlays a mask on the oscilloscope display. The procedure followed in the operation of an AUTOSET TO MASK function is to set the horizontal and vertical scales to a nominal value, acquire a waveform, and adjust the scale and position of the waveform by adjusting the settings of the input A/D converters, and display the mask.
After an AUTOSET TO MASK function sets up the acquired waveform and displays the mask, the telecom mask testing software checks for intrusions into the mask area by the waveform being tested (i.e., violations, or mask hits) that would indicate that the waveform does not comply with applicable telecommunications standards.
For many telecom applications it may be desirable to xe2x80x9czoom-inxe2x80x9d on the display near the area (i.e., magnify the area) in which a violation occurred so that the user could perform a closer examination. Unfortunately, prior art telecom mask testing arrangements do not exhibit this capability for reasons to be explained below.
What is needed is a solution that allows the mask and the waveform under test to be xe2x80x9clocked togetherxe2x80x9d for horizontal and vertical repositioning, and xe2x80x9czoomedxe2x80x9d (i.e., magnified) for closer inspection.
A telecom mask testing zoom function draws mask. pixels into a raster memory. In this way, the mask is treated as a waveform. Comparison of the mask pixels and waveform pixels to detect collision between a waveform pixel and a mask pixel (i.e., a mask violation) is performed substantially in real time, as the pixels are being composited into the raster memory by the rasterizer. The mask is scalable and repositionable by the rasterizer under control of a controller, because it is treated as a waveform. The mask is lockable to the waveform because both are stored in pixel form in raster memory by the rasterizer under control of the controller.